1. Field of the Invention
The present invention relates to a coolant tube for a holder for a tool having a tapered hollow shaft with an upper opening for clamping into a tool receptacle, wherein the coolant tube is arranged in the interior of the tapered hollow shaft for supply of coolants to the tool, and the coolant tube has an inlet opening for coolants, said inlet opening facing the upper opening, and an upper tube section which, when the holder is clamped in the tool receptacle, projects into a supply tube for coolants, said supply tube overlapping the coolant tube at least partially, whereby a covering is provided for the inlet opening, which prevents chips from entering into the coolant tube.
The invention further concerns a holder having a coolant tube of this kind.
2. Related Prior Art
Such a holder with coolant tube is known from DE 196 21 240 A1.
These holders, which are also called HSK tool holders, consist substantially of three sections, namely the tapered hollow shaft, adjoining which at the bottom is a thickened collar on which gripper grooves for automatic tool changing mechanisms are provided. Adjoining said collar at the bottom is a holding shaft onto which a variety of tools can be attached. Since some of said tools in operation must be cooled with coolant, a centered, stepped threaded hole is provided in the interior of the tapered hollow shaft into which hole a coolant tube can be threaded. Said coolant tube has a central coolant conduit through which the coolant coming from the machine tool arrives at the respective tool.
Tool holders of this kind, or HSK tool holders, are standardized, they can be fitted with various tools and then clamped into a tool receptacle, which is provided in a spindle of a machine tool and has an opening complementary to the tapered hollow shaft.
The tapered hollow shaft is equipped with an upper opening through which jaw segments and the draw-in taper of a clamping system can engage into the interior of the tapered hollow shaft. Clamping of the tapered hollow shaft into the receptacle is accomplished by the fact that the jaw segments, in their released position, are first swung inward and inserted, together with the draw-in taper, through the opening into the tapered hollow shaft. The draw-in taper is then pulled partly back out of the tapered hollow shaft via its draw-in rod, thereby pressing the jaw segments outward in their clamping position, in which they rest against the interior of the tapered hollow shaft and clamp the latter nonrotatably to the spindle.
When the holder is inserted into the tool receptacle, the coolant tube enters a centered bore, provided in the draw-in taper and the draw-in bar, through which coolant is then delivered during operation. Provided in the front region of said bore is a sealing ring, preferably an O-ring, which comes into contact with the cylindrical outer enveloping surface of the coolant tube.
In machine tools, problems repeatedly occur in connection with the supply of coolant to the tools. Coolant supply is often interrupted by clogged coolant conduits in the tools themselves or influenced disadvantageously by the fact that the seal between the coolant tube and the coolant delivery system on the machine tool becomes leaky, so that coolant pressure declines and is no longer sufficient to push coolant into the small coolant conduits in the tools. A diminution in the coolant supply due to clogged coolant conduits or a leaking seal often leads, however, to overheating and thus to damage of the tool, so that frequent cleaning of the holder, the coolant tube, and the tools with which the holders are fitted, is necessary. In addition, the sealing ring on the machine tool must be replaced at relatively short intervals. If these time- and wage-intensive actions are omitted, the operational reliability of the machine tools equipped with the holders is reduced.
In the case of the coolant tube mentioned in DE 196 21 240 A1, the problem is remedied by providing a cover for the inlet opening which prevents chips from entering into the coolant tube.
Said cover is designed as a sieve, which rests on a shoulder of the coolant conduit running lengthwise through the coolant tube and which is held by a toothed ring in the upper widened diameter of the coolant conduit.
In operation, it turned out that due to wrong mounting or the pulsating coolant the toothed ring falls out or the sieve is jackknifed, so that the desired protection effect gets lost.
Moreover, it was realized that the sieve is dissolved which also results in a loss of the protection effect.
Therefore, in EP 0 925 869 A2, a further development is described, in which at the top of the coolant tube an insert is arranged on which various sieves are provided. Said insert is held by a toothed ring in the coolant conduit.
By a sequence of fine sieves which are supported by coarser sieves it shall be prevented that the fine sieve is pushed into the coolant conduit.
It has turned out, however, that here, too, the toothed ring falls out or due to mounting problems the insert and/or the toothed ring are wrongly inserted or get lost already on transport, so that the desired protection effect is not reached.
In view of the above, it is an object of the present invention to improve the coolant tube in such a way that the disadvantages mentioned above are avoided. In particular, the operational safety of a machine tool with a constructively simple design and equipped with a holder with a coolant tube, as mentioned at the outset, is to be ameliorated.
According to the invention, this object is achieved with the holder and the coolant tube mentioned at the outset by providing in the coolant tube an exchangeable insert tube which holds the cover.
The object of the invention is in that way completely achieved.
The insert tube, which preferably runs through the coolant tube in its complete length, diminishes the clear width of the coolant conduit, so that it was originally assumed that the pressure applied to the cover was enforced and, thus, the danger of malfunction increased. In contrast, it turned out, however, that this was not the case. It turned out, namely, that, via the insert tube, a distinctively better support of the cover can be achieved, which now e.g. can be inserted between the upper end of the coolant tube and the insert tube, so that a toothed ring is not necessary any more.
It turned out, namely, that the toothed ring, which is used in the prior art for fixation of the cover, is one of the reasons for detaching covers. The toothed ring can namely not, as assumed, get jammed in such a way at the surface of the coolant tube that it is fixed in a safe position. The coolant tube is namely manufactured from hardened metal, so that the toothed ring cannot penetrate into the hardened surface.
Since the coolant tube is now completely interspersed by an insert tube, the clear width of the coolant conduit is reduced on the whole length of the coolant tube compared with the prior art, which, however, against all expectations, has neither resulted into problems.
It turned out, namely, that with the counter pressure of 70 bar occurring in operation, the transporting capacity of the coolant pump of 201/min still passes through the coolant tube, so that a sufficient coolant flux is ensured. If the tube, however, is run without counter pressure, so to speak in no-load operation, the transporting capacity is distinctively diminished by the insert tube additionally provided, what, originally, seemed to be against the use of such an insert tube. It turned out, however,xe2x80x94as mentionedxe2x80x94that the reduction of the cross-section of the coolant conduit is no problem during operation.
In a further development it is preferred if the coolant tube has on its top a rim which protrudes to the inner side.
This proceeding has the advantage that the cover is jammed between the protruding rim of the coolant tube and the insert tube, so that it is held in a safe position and cannot be detached. Another advantage is that the cover is held by the front surface of the coolant tube, so that it has a safe support.
Another advantage is that the cover must now be inserted into the coolant tube so to speak from behind, whereupon the insert tube is inserted. In that way, wrong mounting is not possible any more, because, if the cover gets jammed in the coolant tube, the insert tube cannot be inserted any more, and that means that the coolant tube cannot be fixed to the tool holder. In that way, wrong mounting is prevented.
On the other hand, it is preferred if the cover is fixed to the insert tube.
This measure has the advantage that the mounting of the cover on the insert tube is independent of the mounting of the cover on the coolant tube, latter is now done namely by simple insertion of the insert tube into the coolant tube. The requirements to the insert tube are completely different from the requirements to the coolant tube, so that the insert tube can be designed in such a way that the cover can be safely fixed to it.
It is also in this way that the safety problems from the prior art are overcome.
Generally, it is preferred if the cover has at least one sieve, whereby the insert tube further preferably has a centric coolant conduit, the inner diameter whereof widens step-like in the area of the inlet opening, while forming a shoulder, whereby the sieve rests on the shoulder.
Not only is this measure constructively advantageous, it also permits a simple fixation of the cover, i.e. the sieve, on the insert tube. The sieve is namely merely inserted from the front into the insert tube and held there for example with a toothed ring.
When doing so, it is preferred if the insert tube is manufactured from a softer metal than the coolant tube, preferably of brass.
The advantage here is that for example a toothed ring can distinctively easier and firmer be jammed in the coolant conduit in the insert tube than it is the case in the coolant tube itself.
In that measure, it is further preferred, however, if the insert tube is flanged at its top and the cover is jammed between the flanged top and the shoulder.
This measure ensures an even better fit of the cover in the insert tube and prevents, moreover, wrong mounting.
The cover, i.e. the sieve, is now placed from above onto the shoulder in the insert tube, after which the upper end of the insert tube is flanged. By said flanging, the sieve is safely held in the insert tube.
Should problems arise while mounting of the sieve on the insert tube for the reason that the sieve gets jammed, the flanging would not be sufficiently possible. Even if said failure is not realized during the manufacturing of the insert tube equipped with the sieve, it will be realized at the latest when the insert tube is inserted into the coolant tube and cannot be fitted there completely due to lacking of flanging or reversing at its top.
Said measure so has several advantages, one is that a constructively simple construction is chosen, the other is that it is, additionally, fail-safe because only if the sieve is correctly mounted in the insert tube, the latter can be completely inserted into the coolant tube.
Generally, it is preferred if the coolant tube has a flange on its lower end, by means of which it is screwed by means of a coupling nut with external thread to the holder.
Said measure is known per se, it has the advantage that the coolant tube can be exchanged. In that way, it is possible to replace the old coolant tube in existing holders by a coolant tube according to the invention.
It is further preferred if the insert tube has a flange at its end remote from the inlet opening, by means of which it is jammed between the flange of the coolant tube and the holder.
Said measure is constructively advantageous because it allows a safe fixing of the insert tube, without further mounting steps being necessary. When mounting the holder according to the invention, it is now merely required to insert the insert tube from behind into the coolant tube and then to fix the coolant tubexe2x80x94as usualxe2x80x94to the holder by means of a union nut.
Even further, it is preferred if there is supported on the sieve another sieve with finer mesh size.
Said measure is known per se, it ensures that on the outer side, i.e. facing the supply tube, a finer sieve rests, which even filters finest chips, and which is supported by a coarser sieve, so that it does not bend to the inside even when there is heavily pulsating coolant or clogging occurs.
Further advantages can be taken from the description and the enclosed drawings.
It is to be understood that the features mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.